1. Field of the Invention
The present invention, relates to an on-hoard radar apparatus, an object detection method, and an object detection program.
2. Description of Related Art
Recently, for the purpose of improvement of convenience or safety in vehicles such as automobiles, an on-board radar apparatus using a millimeter-wave radar as a detection device has been increasingly mounted on vehicles.
Particularly, an FMCW (Frequency-Modulated Continuous Wave) system capable of simultaneously acquiring a distance and a relative velocity to a target object (object) is generally used as a detection technique in the longitudinal direction. Techniques such as detection of an azimuth of a target object using a DBF (Digital Beam Forming) method or separation of target objects using a MUSIC (Multiple Signal Classification) method are generally known as a detection technique in the transverse direction.
Here, such an on-board radar apparatus is mounted on a front part of a vehicle so as to emit radio waves (transmission waves) to the front side of the vehicle and to detect (sense) information on target objects present on tire front side of the vehicle.
Beat signals are generated by receiving reflected waves from a reflecting object (target object) by the use of an antenna array in which receiving antennas are arranged and mixing the received signals by the use of a mixer. Thereafter, frequency components relevant to the reflecting object are extracted by converting the beat signals to digital signals through the use of an A/D (Analogs-Digital) converter and processing the digital signals by an FFT (Fast Fourier Transform). The relative velocity and the distance to the target object are calculated by the combination of the frequency components extracted from an ascending section and a descending section in modulation frequency.
In the on-board radar apparatus, the azimuth of the target object is calculated by detecting an azimuth using signal processes such as a DBF or a high-resolution algorithm on the frequency components relevant to the reflecting object.
In the on-board radar apparatus, examples of the reflecting object include a vehicle, a pedestrian, and a motorcycle. When the reflecting object is a pedestrian or a motorcycle, the reflecting sectional area thereof is smaller than that of a vehicle and thus the amplitude of a reflected wave is smaller than that of a vehicle. Accordingly, when reflected waves are acquired with the same gain, the generated heat signals may be saturated or the heat signals may be buried in noise so as not to detect peak signals, whereby the on-board radar apparatus may not detect the reflecting object.
Accordingly, in Japanese Unexamined Patent Application, First Publication No. 2010-112937 A (Patent Document 1), a relative velocity and a relative distance to a reflecting object are detected by generating peak signals using different gains in first and second transmission and reception periods.